Color grading is the process of altering and enhancing the color of a motion picture, video image, or still image either electronically, photo-chemically or digitally. Modern color correction, whether for theatrical film, video distribution, or print is generally done digitally in a color suite.
Regarding today's digital cinema technology, any image of the cinema will experience a plurality of different systems from image acquisition to the final projection. For example, at first, the images captured by a digital camera are needed to be graded with a color grading system, and then, the graded images are recorded into films through a film recorder. Finally, the images are projected to screen via a projection system. However, since each projection system has its own unique color space, same images would be shown out in difference via different projection systems. Therefore, a task of color management in such projection systems is to recognize the characteristics of the color space thereof, so as to unify the color space in different systems. In simple terms, the task of the color management is to ensure the image during production is substantially consistent with the images shown on the terminal screen.
In general, the process of the color management can be recognized as a color conversion process in different color space. Without color correction, a same image will be seen in large difference for different color spaces, i.e. the images shown on the monitor is very different from the images shown on the final screen. Besides, significant visual difference will appear between different monitors and different projection environment. In absolute terms, there is no two color space systems are exactly the same in the world. At present, the role of the color management systems appeared in the market is to minimize the visual difference of images between different media and display devices. The most important element for this role is unifying the images shown on the monitor during digital color grading process with the images shown on the final screen copied from the film, to make them “look” more similarly. It is the only way to provide a relatively “accurate” visual reference for color grading staffs. In theory, such kind of color space conversion is often completed by LUT (Look Up Table).
The LUT is a bridge to connect different color spaces in the process of color management. The LUT can feed back an output value in accordance with an input value. For example, in a color space 1 with 10 bit RGB, a red color is expressed as R=640, G=102, B=94, and this red color also exists in another color space 2 with 10 bit RGB, but is expressed as R=600, G=90, B=145. Then, the LUT which converts the color space 1 to the color space LUT 2 will feed back the value of R=600 , G=90, B=145 after reading the data of R=640, G=102, B=94.
One feature of the LUT is that, it can perform the color correction for different display devices without changing the original file. The benefit by this way is the original images are not processed and accordingly will not be damaged. And furthermore, a lot of rendering time will be saved since without changing the original images.
However, the existing LUT color grading process is very complicated. In order to achieve color grading functionality, an additional color grading cartridge is often required to do the color grading processing with the LUT data which is generated from an application software. That is to say, in the prior technology, the monitor includes an LUT module, and the color grading cartridge also includes an LUT module, wherein the LUT module of the monitor is used to implement the mapping of color space, and the LUT module of the color grading cartridge is used to do the color grading processing. As such, the integration of the system is low.